The continuing development and evaluation of new radiopharmaceuticals with a high organ specificity, high photon yield, and low patient dose is of utmost importance in nuclear medicine. Radiopharmaceuticals tagged with short lived radionuclides which have ideal physical and imaging characteristics (e.g. Tc 99m or In 111) for kidney evaluation have not been sufficiently explored. A major breakthrough has yet to be achieved in the continuing search for such a renal agent. Radionuclide labeled compounds which are currently available for use in man, including Hg 197 chlormerodrin, I131- orthoiodohippurate, Tc 99m-DTPA and others are not ideal either because of the suboptimum energy of the radionuclide label for use with imaging equipment or relatively high radiation dose, or slow rate of excretion with inadequate organ specificity. The project described here is designed for studying Tc 99m and other short lived radionuclides, In 111, Pb203 complexed with various agents including oxine and its sulfonic acid derivatives, penicillins and analogs of hippurates with known or anticipated excretion from the body primarily by the kidney. Agents will be sought which are added to the urine by renal tubular secretion as well as by glomerular filtration. This program should lead to the development of an agent with the desired characteristics of providing a high target to background ratio with a short effective half life and minimal patient radiation dose for renal functional evaluation and imaging.